There is a conventionally-known spectral measurement apparatus configured to irradiate a sample as a measurement object with excitation light and detect light to be measured. As a technology of this kind, for example, Patent Document 1 describes the absolute fluorescence quantum efficiency measurement apparatus configured so that, in obtaining a quantum yield, the sample is fixed at a position where it is not directly hit by the excitation light, in an integrating sphere, and a light absorptance of the sample is obtained from an intensity obtained with indirect incidence of the excitation light to the sample and an intensity obtained with direct incidence of the excitation light to the sample.
Furthermore, for example, Patent Document 2 describes the quantum efficiency measurement apparatus configured to measure the excitation light absorbed by the sample in a state in which the excitation light after passage through the sample is reflected in an integration space and to measure light generated from the sample in a state in which the excitation light after passage through the sample is not reflected in the integration space. This quantum efficiency measurement apparatus performs the two stages of measurement processes, thereby to reduce measurement error due to re-excitation (secondary excitation). Non Patent Documents 1 to 3 describe calculation of quantum yields on the premise that the excitation light is made incident to the sample so as to be included in the sample.